1. Field of the Invention
Embodiments of the invention relate to the field of communication, and more specifically, to in-phase and quadrature imbalance calibration.
2. Description of Related Art
Radio frequency (RF) receivers or transmitters employing direct conversion architectures generate in-phase and quadrature (I-Q) analog signals. These signals usually have distortions which limit demodulator or modulator performance. These distortions, called quadrature errors, are caused by the gain and phase imbalances between the I-Q signal components. Imbalance in I-Q signals may induce an image frequency and direct current (DC) offset which interfere with the demodulation or modulation process. To correct the I-Q imbalance, it is necessary to calibrate the communication subsystem. Existing calibration methods typically utilize iterative approaches. These techniques correct the phase error, then the gain error, repeatedly in iterative sweeps.
Existing calibration techniques have a number of disadvantages. First, the iterative approach requires multiple processing passes, resulting in long processing time. This long processing time may cause a communication receiver or transmitter to be out-of-service. For communications services requiring constant bit rates, such as telephony or real-time video, the out-of-service interruption may cause undesirable performance. Second, the iterative nature of the technique is not accurate and achieves poor results, leading to degraded performance.